In spinal deformity surgical procedures, the curvature of the spine (e.g., the coronal curvature of the spine and/or the sagittal curvature of the spine) can be corrected by the implantation of a construct of bone anchors and spinal fixation elements. Examples of bone anchors used in such a construct include hooks and bone screws. An examples of spinal fixation elements used in such a construct is a rod
During one type of spinal surgery, a surgeon first exposes the posterior spine and attaches bone anchors to selected vertebrae of the spine. The surgeon then inserts a spinal fixation element into receiving portions of the bone anchors to connect the selected vertebrae, thereby fixing the relative positions of the vertebrae.
Generally, a controlled mechanical force is required to bring together the spinal fixation element and a bone anchor in a convenient manner. This procedure is typically referred to as “reduction.” To complete a reduction, a surgeon must insert a locking mechanism, such as a set screw, into the vertebral anchor to lock the spinal rod to the implant before the force for inserting the rod can be removed.
In addition to correcting the curvature of the spine, the angular rotation of one or more vertebrae relative to other vertebrae may also be corrected. Conventional surgical procedures for correcting the angular rotation of a vertebra involve rotating the spinal fixation element, for example, a spinal rod, connected to the vertebra by a bone anchor. In the case of constructs that include a spinal rod, this procedure is typically referred to as “vertebral body derotation.” Vertebral body derotation can place significant stress on the interface between the bone anchors connected to the rotated spinal rod and the vertebra in which each bone anchor is implanted. This stress can cause a failure of one or more of the bone anchors or harm to the vertebra. Accordingly, there is a need for improved instruments and methods for manipulating a vertebra.
Conventional derotation instruments are designed to be used after reduction has been performed and the spinal fixation element has been secured to the bone anchor. However, the bone anchors often bind on the fixation element during the rotation, preventing the motion or requiring significant force to obtain it. Thus, in some instances it may be beneficial to perform derotation before reduction. In addition, reduction and derotation require different instruments. Thus, one instrument must be removed to allow the other to be used.